This application relates to a gel-forming insert for use in forming electrophoresis microgels of the type which can be used in medical diagnosis, especially for the sequencing of nucleic acids, and to methods of making and using such gels.
International Patent Publication No. WO93/00986 describes electrophoresis gels with a thickness of 25 to 250 microns. The gels are formed between two clamped-together plates, one of which is grooved to a depth equal to the desired gel thickness to form parallel tracks which are then filled with gel. Other formats for very thin electrophoresis gels are described in the parent application, U.S. Pat. No. 5,627,022, and in commonly assigned U.S. Pat. Nos. 5,599,434 and 5,618,398, which are incorporated herein by reference.
In utilizing thin electrophoresis gels, an important challenge is the introduction of a significant number of samples at defined locations along the starting edge of the gel. U.S. Pat. No. 4,929,329 discloses the use of a comb to define a plurality of sample-receiving wells in an electrophoresis gel as is hardens or to cut a plurality of wells into the top surface of an already hardened gel. Formation of sample wells using a comb included during the hardening process requires the subsequent removal of the comb, which can result in damage to the gel structure if not carefully carried out, and this risk increases as the thickness of the gel decreases. Similarly, cutting wells into an already hardened gel may result in a lack of uniformity which will negatively impact on gel performance.
U.S. Pat. No. 5,281,322 discloses an electrophoresis cassette in which so-called "well spacers" are used to define the wells. These spacers are integral extensions of the plates defining the gel arranged in a line along one edge of the plates. Sample wells are formed by filling the area between the plates to such an extent that the gel extends only partially into the space between adjacent spacers. This approach avoids potential damage to the gel due to the insertion or removal of a well-forming comb, but has its own limitations. In particular, the size of the wells is limited to those into which gel-forming solution can be reproducibly introduced, since variations in the depths of the wells or unevenness in the gel surface within a well can result in electrophoresis results which are difficult to interpret.
It would therefore be desirable to provide an apparatus for defining sample introduction locations in an electrophoresis gel which provides very consistent and reproducible well structures and which does not lead to significant instances of gel destruction. It is an object of the present invention to provide such an apparatus.